Picking assistant systems, which instruct a worker on which of various articles (such as parts and goods) stocked in a shelf the worker should pick up, are widely used in production lines and logistics bases. In one example, a picking assistant system is used in a production line to instruct a worker on parts to be assembled to a target product and the number thereof, out of various parts stocked in a parts storage (typically, a parts shelf). In another example, a picking assistant system is used in a logistics base to instruct a worker on goods to be put into a target shipper (container) and the number thereof, out of various goods stocked in a goods storage (typically, a goods shelf).
A picking assistant system includes display devices used to provide a worker with instructions. Most conventionally, lamps and segment displays have been used as display devices of a picking assistant system. In recent years, it has been proposed to use a projector as a display device of a picking assistant system. For example, M. Hashimoto et al. “Application of Mixed Reality Technology to Order Picking for Warehouse Storage (2)”, proceedings of 19th Virtual Reality Society of Japan Annual Conference, September 2014, pp. 553-556 (non-patent literature 1) discusses merits and demerits of a wearable projector and a desktop projector in assisting a sorting work.
One requirement imposed on a picking assistant system is to prevent operational errors. Various mechanisms have been proposed to prevent operational errors. For example, Japanese Patent Application Publication No. 2005-1781 (patent literature 1) discloses a picking assistant system configured to measure the weight of goods put in each shipper and determine whether correct goods are put in each shipper, on the basis of the measured weight. Furthermore, Japanese Patent Application Publication No. 2006-321590 (patent literature 2) discloses a picking assistant system configured to detect the position where a hand of a worker passes through the opening of a goods shelf by using infrared ray, and assert an alarm when the detected position is not proper.